The invention relates to an anchor consisting of solid material for concreting or embedment in heavy loads, such as precast concrete members.
For the transportation of heavy loads, such as in precast concrete members, prefabricated multi-layer slabs, unitized units, facade linings, supports, spandrel units etc., it is known to embed anchors of steel or iron in the precast concrete member, in such a way that the head of the anchor protrudes from the surface of the concrete member for the engagement of a coupling part of the hoisting tackle. At the same time, the head of the anchor is usually embedded in the precast concrete member in such a way that it lies in a depression provided in the precast concrete member, so that the anchor head does not project beyond the surface of the concrete member. Transport anchors of this type are fabricated from round or flat steel or iron and have an upset round head and foot for load absorption. Anchors of flat steel have on the projecting head part a recess, namely a hole for the coupling of the hoisting tackle. In a known, customary design, the foot part embedded in the concrete is provided with an expansion element for introduction of the load into the concrete, which expansion element is formed by slitting the flat material in the foot part and by bending apart in opposite directions the expanding legs produced by the slitting. The production of this well known anchor is, however, in each case cross-sectionally dependent on the magnitude of the moment of resistance occurring because, depending on stressing, there must always be an adequate cross-section of the anchor to avoid a bending back of the expanding legs under the effect of the load and thus a tearing out of the concreted anchor. It is therefor necessary when dimensioning such an anchor provided with an expanding foot to maintain a minimum cross-section specified for the load envisaged in a particular case, in particular a minimum thickness, to counter the risk of the anchor tearing out.
Round anchors with widened feet and flat anchors with bent-off expanding feet must, in addition, be embedded in the precast concrete member to a load-dependent minimum embedded depth. The greater the load to be absorbed, the deeper the foot of the anchor must be anchored in the concrete member. In addition, an adequate depth of the foot provided with expanding extensions must be maintained during concreting in order to create as great a saddle bearing load as possible and thus a correspondingly large breakout cone in the concrete of the precast member. Furthermore, expanding anchors require a larger design length from the outset as the expansion of the foot caused by separation of the flat material impairs its strength, especially as the incision must be relatively deep to avoid an excessive deformation of the expanding legs during bending.
With thin precast concrete members it is a further disadvantage, for reasons of strength, that both in the case of round anchors with round expanding extensions in the foot and in the case of flat steel expanding anchors with expanding legs which are bent off in opposite directions and offset relative to each other, the forces entering the precast concrete member via the anchor are not precisely directed into the concrete when they are introduced.
It is also known to produce anchors of the generic type in cast steel design, reference being made to U.S. Pat. No. 4,437,642. However, production by this method is elaborate and expensive since for each application load a new mold is necessary, and individual design in particular of the expanding extensions corresponding in shape, size and position with respect to the anchor shank in an application case deviating from the standard size is technically difficult and not economically justifiable. In addition, production from cast iron entails the risk of shrinking; any shrinkage cavities are not externally detectable; so that the finish-cast anchor would have to be subjected to special and elaborate material tests owing to the high safety requirement in the transportation of heavy loads.
For thin precast concrete members it is further known to use so-called two-hole anchors of flat steel which are intended to ensure a deeper introduction of the load into a thin precast concrete member. The head part of such two-hole anchors is designed in the same way as with round or flat anchors. In the foot part, on the other hand, there is a round or oval hole, through which a so-called secondary iron is threaded before concreting, which lies transverse to the longitudinal axis of the transport anchor and is intended to introduce the load forces on either side over a relatively long path deep into the precast concrete member.
In order to be able to thread the secondary iron quickly and simply before concreting, the hole in the foot part of the two-hole anchor must have a correspondingly large clearance. In addition, the secondary iron must have an adequate length, namely up to 10 times the actual anchor length, to achieve its secure anchorage. These requirements necessitate a relatively high amount of material and cost expenditure, especially as the separate threading of the secondary irons requires an additional, relatively complex operation.